Nitrocarburising

Nitrocarburising is a variation of the case hardening process. It is a thermochemical diffusion process where nitrogen, carbon, and to a very small degree, oxygen atoms diffuse into the surface of the steel part, forming a compound layer at the surface, and a diffusion layer. Nitrocarburising is a shallow case variation of the nitriding process. This process is done mainly to provide an anti-wear resistance on the surface layer and to improve fatigue resistance.

Benefits of nitrocarburising

• Relative low cost;
• High resistance to wear;
• Excellent scuffing and seizure resistance;
• Fatigue properties improved by up to 120%;
• Considerably improved corrosion resistance;
• Good surface finish;
• Negligible shape distortion;
• Predictable growth characteristics; and
• Alloy substitution – plain carbon steels replacing low alloy steels.

Application & materials

Advantages of the process include the ability to harden materials which are not pre-hardened, the relatively low temperature of the process which minimises distortion, and relative low cost in comparison to carburising or other case hardening processes.

Typical industries:

Oil and gas, valve, pump, agriculture equipment, automotive, stamping, textile, extrusion and injection moulding, and firearms components.

Typical parts:

• Oil and gas – gears and pinion shafts
• Valve components – gates, seats, balls, stems, regulator valves
• Pump components – impellor housings, bodies, plungers, cylinders
• Agriculture equipment – harvesting combine cutters, separators, crop transfer, chopping components
• Automotive – diesel engine oil pumps, gears, crankshafts and camshafts
• Stamping – dies, tooling
• Textile – grooved drums
• Extrusion and injection mould – moulding augers, barrels, die components
• Firearms – slides on automatic firearms

Nitrocarburising can be applied to the same materials as in nitriding, as well as unalloyed materials, where good wear resistance and some improved fatigue resistance are needed at a low cost. It is widely used for stampings, as an alternative to hard plating.

Nitrocarburising process details

Nitrocarburising is carried out at sub-critical temperatures and involves the diffusion of nitrogen and carbon into the surface of carbon steel to give a somewhat harder case and soft core with a very thin compound layer on the surface.

The compound layer is wear and corrosion resistant and yet is not brittle, unlike its counterpart in the nitriding process. Since it provides an essential part of the properties required from the process it must not be removed by subsequent machining. Below the compound layer, the thin case significantly enhances the fatigue resistance of the component.